Cardinal Points

Question 1

The cornea, if it were surrounded by air would have an optical power of ..

Answer 1

-5.2D

Question 2

The most important factor that the cornea is a strong plus lens is…

Answer 2

the fact that the posterior surface is surrounded by the aqueous, with nearly similar refractive index

Question 3

ray diagrams of thick lens

Answer 3

there are 2 refractions

Question 4

principle plane

Answer 4

every thick lens has two principal planes (H’ and H)

• paraxial approximation
• not always inside the lens

Question 5

What is reported when ordering ophthalmic lenses?

Answer 5

effective focal length

Question 6

Front Focal Length (FFL)

Answer 6

the distance along the length of the optical axis that separates the focal point in the object space from the vertex V of the first surface

Question 7

Back focal length (BFL)

Answer 7

the distance along the length of the optical axis that separates the back point in the object space from the vertex of the second surface

Question 8

Principal points summary

Answer 8

• a thick lens or lens system has two principal points, both located on the optical axis
• the planes perpendicular to the optical axis at the principal points are termed principal planes
• by employing these planes, we handle any thick lens as a thin

Question 9

Nodal Points

Answer 9

parallel displacement

Question 10

6 cardinal points

Answer 10

• 2 focal
• 2 principal
• 2 nodal points

Question 11

cardinal points: focal points

Answer 11

-collimate a beam from the primary focal point or converge a collimated beam to the secondary focal point

Question 12

cardinal points: principal points

Answer 12

preserve ray displacement. Act as if thin lens

Question 13

cardinal points: nodal points

Answer 13

preserve angle with optical axis